HEFEI, China (Reuters) - The woman at the centre of China's most politically explosive trial in three decades did not contest charges of murder on Thursday in a hearing that lasted just seven hours and could determine the fate of former Politburo member Bo Xilai.

A formal verdict will be delivered at a later date, a court official said, recounting details of the closed-door hearing.

Bo's wife, Gu Kailai, chose not to contest the charge of murdering British businessman Neil Heywood whose alleged secretive dealings with the couple fuelled a scandal exposing the intimate nexus between money and power in China's elite.

The dramatic account of Heywood's death by poisoning is also likely to sound the final death knell to Bo's political career, even as sympathisers cast him as the victim of a push to oust him and discredit his left-leaning agenda.

"The accused Bogu (Gu) Kailai and Zhang Xiaojun did not raise objections to the accusations of intentional homicide," the official, Tang Yigan, said after the hearing, referring also to Gu's co-accused, an aide to the family.

State television showed Gu, wearing a dark pant suit and a white shirt, being led into the courtroom and being seated in the dock. She appeared to have put on weight since she was detained earlier this year.

The court official quoted prosecutors as saying Gu and Zhang had killed Heywood with a poisoned drink in far southwestern Chongqing last November, after a business dispute between Gu and Heywood. Bo ruled the vast municipality until he was sacked in March just before the murder scandal burst into the open.

As a result of the dispute with Heywood, Gu had become convinced Heywood was a threat to her son, Bo Guagua, the official said without elaborating.

"Gu Kailai believed that Neil Heywood had threatened the personal safety of her son Bo (Guagua) and decided to kill him," the official added, reading from a statement to a packed news conference of dozens of reporters who had been barred entry to the courtroom in the eastern city of Hefei.

The aide, Zhang, had driven Heywood to Chongqing last November from Beijing and prepared a poison which was to be put later into a drink of water. Later that day, Heywood met Gu at a hotel, he became drunk and then asked for water.

"She poured a poison into his mouth," the official said.

GU MAY AVOID DEATH PENALTY

Gu and Zhang face the death penalty if convicted. But many legal experts expect Gu will be convicted but only sentenced to a lengthy jail term, citing her desire to protect her son, who graduated from Harvard this year, as a mitigating factor.

Gu's state-appointed lawyer told the court on Thursday that Heywood himself had some "responsibility in the matter", the court official said, adding that a Heywood family representative had voiced respect for the court during the hearing.

In London, family members declined to comment on the case.

Britain's Foreign Office also declined to comment until the outcome of the case. It said two British diplomats had attended the trial "to observe the proceedings and fulfill consular responsibilities to the Heywood family", a spokesman said.

As the trial took place, police dragged two Bo supporters into an unmarked car after they appeared outside the courthouse, singing patriotic songs that were the trademark of Bo's populist leadership style and condemning the trial as a sham.

"I don't believe it. This case was decided well in advance," Hu Jiye, a middle-aged man wearing a T-shirt and baseball cap, told foreign reporters at the rear of the court building, which was cordoned off by dozens of police standing in heavy rain.

Hu and his friend were then shoved by plainclothed police into a car. His companion, also a middle-aged man, struggled, yelling "Why are you taking me? Why are you taking me?"

State censorship of Internet chatter on the trial was swifter than normal on Thursday, with users of China's popular Twitter-like service Sina Weibo playing cat and mouse with censors to discuss the case, using word play to try and get around the controls.

COVER-UP ALLEGATIONS STALK BO

In sketching out the case against Gu for the first time, the court official also revealed that four Chinese policemen had now been charged with trying to protect her from investigation - a development that could prove dangerous for Bo, who has so far not been charged with any criminal offence.

Police sources in Chongqing have said that the former Politburo member tried to shut down the investigation into his wife after being told she was a suspect.

Bo and Gu have been in detention and have not made any comment since Gu was officially accused of murder in April. Bo's supporters see it as part of an attack on his populist brand of politics in Chongqing, which appealed to many of the party's leftists but was seen as dangerous by his enemies in Beijing.

Gu, herself a career lawyer, was defended by a state-appointed lawyer with meagre experience in criminal cases.

The state decided who was to represent Gu, denying her the use of a family lawyer - a move that prompted Gu's 90-year-old mother, Fan Chengxiu, to recently complain to the Justice Ministry, according to a source close to the family.

"The answer (from the ministry) was that the legal process did not have to be fully carried out in this case and that Fan should stop pestering them," the source said.

The trial of Gu, glamorous daughter of the ruling Communist Party aristocracy, is the most sensational since the conviction of the Gang of Four more than 30 years ago for crimes during the 1966-76 Cultural Revolution.

But despite British calls for the case to be handled fairly and to unearth the truth around Heywood's death, her defence was entrusted to two provincial lawyers.

The two lawyers, Jiang Min and Zhou Yuhao, could not be reached for comment but a search of public information showed the more senior attorney, Jiang, is a specialist in financial cases and that neither has any obvious connection to the Bo family.

YOUNGER BO

Bo and Gu's son, who is believed to be still in the United States after graduating from Harvard this summer, told CNN in an e-mail that he had submitted a witness statement to the court.

"I hope that my mother will have the opportunity to review them," added Bo Guagua. "I have faith that facts will speak for themselves." CNN said he did not elaborate.

The trial and sentencing of both Gu and Zhang are widely seen as a prelude to a possible criminal prosecution of Bo, who is being detained for violating party discipline - an accusation that covers corruption, abuse of power and other misdeeds.

Bo, who was a favourite of party leftists by promoting himself as a friend of the poor and an enemy of corruption, was sacked as Chongqing party chief in March after his police chief, Wang Lijun, identified Gu as a suspect in Heywood's death.

On Thursday morning, there was no sign of Gu's elderly mother, nor of any members of Heywood's family in or around the courtroom.